In a typical three-phase electric energy meter current input signals for the three phases come from current transformers and voltage input signals from the three phases via resistive voltage divider. The current and voltage input signals are sampled and the current samples are multiplied with the voltage samples to obtain electric energy samples. Accumulating these energy samples provides an indication of consumed electric energy.
In an advanced electric energy meter the current and voltage input signals are converted to digital input samples for further processing by a micro-controller. One straight-forward approach uses separate input channels, for each of the three current and voltage input signals including an analog-digital converter (ADC). In this “synchronous” approach all input signals are processed in parallel and synchronously. An application having a high accuracy requirements over a large dynamic range, such as permitted error less than 1% over a range of 1:2000, high-resolution ADCs of at least 16 bits are needed. These ADCs usually include a sigma-delta modulator followed by a decimation filter. While this approach is successful, it requires a large die space and is expensive. An alternative approach uses a single high-resolution ADC with an input multiplexer and an output de-multiplexer. In this “sequential” approach the current and voltage input signals are sequentially switched to the input of the ADC and the resulting digital samples are corrected in phase to compensate for the delays introduced by the sequential sampling. The sequential approach needs less die space for the ADC but requires a complicated phase adjustment between the successively obtained current and voltage samples.